The Obesity Research Center conducts a multidisciplinary research program focussed on the problem of human obesity. Of its four principal components, one is directed toward the study of eating behavior in nonobese and obese human subjects in an attempt to throw light on the causes of various types of obesity and to obtain greater leverage on the problem of classifying the obesities. To this end, the Center has developed a new device ("universal eating monitor") to show ingestive behavior in lean and obese humans under a variety of conditions. Studies also are being carried out to determine whether obese individuals will defend their excess weight under conditions of covert caloric dilution of a normal-appearing and tasting diet. In the second component, the universal eating monitor is being used to assess the effects in man of various experimentally inserted putative satiety signals. For example, the effect of intravenously given insulin-glucose mixtures and of i.v. cholecystokinin octapeptide on appetitive behavior is being studied in human volunteers. In component 3, metabolic studies continue in an attempt to identify diets with the lowest possible energy content compatible with preservation of body protein and freedom from undesirable side effects. In these studies, special attention is being paid to the effects on body composition and body status of various types of supplemented fasting (e.g. hypocaloric protein diets). Finally, a research-oriented weight control unit for obese outpatients (component 4) has been set up which emphasizes comprehensiveness and thoroughness of workups, new and rational approaches to calorie control and a long-term follow-up procedure designed to help patients maintain their reduced weights.